The present invention relates to fuel injection apparatuses having fuel injectors that inject fuel directly into engine cylinders and methods for controlling fuel injection.
In a typical automotive engine, fuel is injected into an intake passage and mixed homogeneously with air that passes through the intake passage. The homogeneous air fuel mixture is then sent to combustion chambers that are defined in the engine. In each combustion chamber, the air fuel mixture is ignited by a spark plug. This burns the mixture and produces drive force.
The combustion of the air fuel mixture in such homogeneous state is normally referred to as homogeneous charge combustion. In an engine that performs homogeneous charge combustion, a throttle valve is located in the intake passage to adjust the amount of air fuel mixture drawn into the combustion chambers and thus control the engine torque.
However, in engines that perform homogeneous combustion, the throttling action of the throttle valve decreases the pressure in the intake passage. This increases energy losses due to pumping (pumping losses) when the air fuel mixture is drawn into the combustion chambers from the intake passage and thus decreases the efficiency of the engine.
Stratified charge combustion solves this problem. In stratified charge combustion, fuel is injected directly into each combustion chamber. This delivers a rich, highly combustible air fuel mixture to the vicinity of the spark plug. Ignition of the rich air fuel mixture burns the surrounding lean air fuel mixture. In an engine that performs stratified charge combustion, the engine torque is basically controlled by adjusting the amount of fuel injected toward the vicinity of the spark plug. Accordingly, the throttling by the throttle valve is unnecessary. This decreases pumping losses and improves the efficiency of the engine. Furthermore, in an engine that performs stratified charge combustion, the overall air fuel mixture is usually lean. This improves fuel efficiency.
Japanese Unexamined Patent Publication No. 63-246442 describes an engine that performs stratified charge combustion and homogeneous combustion in accordance with the state of the engine. In this engine, a first fuel injector is provided for each cylinder to inject fuel directly into the cylinder. A second fuel injector injects fuel into the intake passage. Fuel is delivered to each injector from a fuel pump.
During the injection of fuel into each cylinder from the associated first fuel injector, normal fuel injection is hindered if the fuel injection pressure of the injector becomes lower than the pressure in the cylinder. This may also cause the compressed, high pressure air in the cylinder to flow into the injector. Foreign matter such as carbon is included in the air. Thus, the entrance of this air, which includes the foreign matter, into the injector may shorten the life of the valve.
Furthermore, the fuel pump uses the torque of the engine as a drive force. Thus, the fuel injection pressure is low when the engine is started. Therefore, there is a greater tendency for air to enter the injector during the starting of the engine.
The engine of the above publication deals with this problem by stopping the injection of fuel from each first injector while permitting the injection of fuel from only the second injector if the pressure in the cylinders becomes higher than the pressure in the associated first injector. As another option, fuel may be injected from both first and second injectors. This shortens the time length during which fuel is injected from first injectors. Accordingly, air is prevented from entering the fuel injector.
However, the structure described in the publication is directed toward fuel injectors that inject fuel into the intake passage. The structure of the publication may not be applied to an engine that is provided only with fuel injectors that inject fuel directly into the associated cylinder.